Color printers and copiers usually operate in work environments that still include black and white devices. While color printing has become increasingly common in the workplace, the cost of color printing still remains substantially above that of black and white printing. Thus, while color documents can be readily created for small volume use, large volume reproduction suggests that black and white printers or copiers should be used.
When a color document is copied to black and white, the information conveyed by the color can be lost. Information is often conveyed by color through the use of distinct colors representing distinct information. When color documents are copied on a black and white copier, or faxed on a black and white facsimile machine, or reproduced from a color file to a black and white print, information may be lost. These devices usually threshold the luminance component of the source image to represent the image in either black or white, raising the problem of translating the intermediate luminance of colored objects on a page. Many darker colors often copy as black, while lighter colors drop out completely. When gray tones are reproduced, they are often mottled or ragged. Ironically, increases in printer resolution and halftone frequency that improve color image quality act to exacerbate the copy problem. Increases in printer resolution make the image appear to the copier as well as to the human observer as smooth areas of intermediate luminance rather than a pattern of halftone dots.
Even if a copier could reproduce the luminance level of source colors reliably, many different colors have the same luminance and are therefore indistinguishable after copying. This may not be a severe problem for pictorial images where much of the information is in the luminance component, but for text or presentation graphics, color offers new dimensions for conveying information. Color can be used to organize important items, distinguish categories, and organize documents and document content. However, when copied or faxed to black and white, the distinguishing capability of color is lost.
The primary goals of most documents is to convey information. If one can anticipate that the document will be copied or faxed with a black-and-white reproduction device, and information might therefore, be lost, it might be desirable to sacrifice some of the appearance of the original document for the sake of information content. One might, for example, decide not to use color at all. Alternatively, a selection may be made to use only color and color features that can be copied well. Such choices are significant barriers in document creation.
It is known that selected background and/or alphanumeric text areas may be printed in repeating and/or varying patterns of highlight color and interposed with black repeating or varying patterns as disclosed, for example, for single pass xerographic printing of composite image security documents in U.S. Pat. No. 5,291,243 to Heckman et al. Some of such color patterns might also reproduce when such documents are copied on a black and white copier, however, such copying is not reliable.
Of further background interest are U.S. Pat. No.5,308,553 to Roetling and U.S. Pat. No. 5,153,576 to Harrington. These patents, however, electronically convert a full color document into a monochrome facsimile for subsequent monochrome printing by electronically converting pixel by pixel the original solid colors into various different patterns of black only images. Such an arrangement, by definition, does not produce originals, which are reproduced in color, for subsequent copying on a black and white copier which retains the informational content of the original color image. Further, the patterns that these methods produce are limited either to a fixed set, or to designs directly controlled by only the three color components and where areas controlled by the different color components do not overlap.
Other patents of interest include U.S. Pat. No. 4,703,318 to Haggerty, which illustrates the idea of forming a character based monochromatic image from a digital representation of a color image by: (1) forming a character based representation of the color image in which a plurality of color characters each describe the background or foreground color within a defined area of the color image; (2) providing a plurality of color pattern masks each corresponding to a color in the color image comprising a pattern of light and dark dots capable of providing in the monochromatic image visual discrimination between areas of different color; (3) transforming the color characters into monochromatic characters by replacing the background and foreground colors of each color character in the corresponding pattern of light and dark dots; and (4) displaying the monochromatic characters on a character based output device. The present invention differs from Haggerty in that the goal is to produce a printed image in which is copyable, and in which colors and shades of colors can be reproduced to maintain the informational content of the original document which used those colors.
U.S. Pat. No. 3,807,852 to Hoydic illustrates an arrangement in which color is used to identify particular identified areas for copying on a black and white copier.
U.S. Pat. No. 5,321,470 to Hasuo et al relates to an arrangement which uses color and the processes of a color copier to prevent forgery of color documents by improper copying.
U.S. Pat. No. 5,138,465 to Ng et al relates to an apparatus and method for producing selectively edited reproductions of the original document in which alphanumeric character codes written using highlighted color arrangements designated treatment to be applied to a particular document.
U.S. Pat. No. 5,153,739 to Laman et al the use of different fonts corresponding to different colors. In such an arrangement, the difference in the font itself provides distinction between different colors which copied in black and white.
U.S. Pat. No. 5,098,817 to Voorhees teaches highlighting of text in a manner which will reproduce when electronically copied. This is accomplished by applying a tone to only that area of the document to be highlighted and so that the tone remains in place during copying. The tone is sufficiently dark so as to highlight text but light enough so that the text is readable.
U.S. Pat. No. 5,142,337 to Karidis et al teaches an arrangement for reproducing gray levels in place of colors in a two color printer.
U.S. Pat. No. 5,568,248 to Wagley teaches that a pattern can be substituted for a color in a document reproduction.
The above-identified references are incorporated herein by reference for their teachings.